This invention relates generally to the field of alignment and more specifically to the extremely accurate alignment of two surfaces relative to each other.
Aligning two surfaces relative to each other to a high degree of accuracy is a problem that is particularly troublesome in devices that require parallel surfaces for efficient operation. Such devices include telescopes, inertial guidance systems and laser cavities. Numerous optical and mechanical approaches have been tried and developed to permit accurate alignment of two or more surfaces. Unfortunately, mechanical approaches have generally failed to be sufficiently accurate for high precision devices and most optical approaches are tedious to apply.
A common optical method used to align parallel surfaces is by means of an autocollimator. Most autocollimators determine the position of a surface or body relative to the autocollimator by projecting a light beam through an optical system onto a reflecting surface. The position of the reflected beam is then observed to determine the position of the reflecting surface. If two surfaces are to be observed, each of the surfaces is observed relative to the reference body rather than to each other.
This use of an artificial reference body introduces some inaccuracies into the measurement system and increases the chance of errors being made in operation of the autocollimator. Also, if a reference body is used, it is very difficult to make real time observations of the relative positions of the observed surfaces during their operation. This is because it is impractical to interrupt operation of many devices in order to check their relative positions.
A real time autocollimator would allow periodic or even constant checks of the parallelism of structures during their operation so that drift due to thermal, vibrational or other changes can be easily corrected. This would be a significant advance, since large optical systems are sensitive to drift due to thermal and mechanical changes that may inadvertently occur during device operation. While small changes of this nature are not harmful to most machines, optical structures such as telescopes always can be greatly degraded if alignment between optical surfaces deteriorates.
In view of the above, the need exists for an easy to operate real time autocollimator capable of measuring relative tilt between two surfaces to high accuracy.